Thermionic tube and heater element therefor



May 16, 1933. s, RUBEN 1,908,792

THERMIONIC TUBE AND HEATER ELEMENT THEREFOR Filed Oct. 22, 1929 FIG.1. 7

" amvewto'c (SAMUEL RUBEN @51 Ivw flbfozmw 1 Patented May 16,

PATENT OFFICE SAMUEL RUBEN, or new roman. Y. assronon To 31mm TUBE comm, or

ENGLEWOOD, new mnsnr, a conrom'rron or DELAWARE Application filed October 22, 1929. Serial No. 401,608.

This invention relates-to thermionic tubes of the heater type, and especially those thermionic tubes adapted to be energized by alternating current. The invention is an i provement upon that described in my. copending application bearing Serial No. 344,876, filed March 6, 1929, particularly 1n that the insulation coating of the heater element is superior to that described in the said application. The material used for such coating and the method of applying it are described in my copending application bearing Serial N0. 398,550, filed October 9, 1929. This insulation material has many advantages over ing to the terms of the invention described in the first of my said co-pending applications, and in combination with the other elements of a thermionic tube, affords superior tube operation. This material has a higher insulation resistance, a lower vapor pressure and is more completely integrated with the base to which it is applied as a coating.

The coating consists ofcrystallized aluminum oxide closely integrated with the heater base material, preferably tungsten, by the decomposition of a halogen compound of the mixture applied. Preferably the filament is insulated with a plurality of separately treatao ed coatings of a mixture composed of an oxide of one of the elements aluminum, magnesium and beryllium and a halogen compound of one of said elements. Its use permits the employment of refractory insulating material without the use of a residual binder. In tubes of the prior art, using a filamentary heater having a flexible coating, there is applied a binder material which is a limiting factor in that it isan inactive component, the presence of which permits current leakages; and if volatilized, the coating is immediately weakened. There being no such binder material in the insulation more fully described in my second mentioned co-pending application, there is a complete absence of leakage or shorts in the herein described tubes, and the coating is able to withstand higher temperatures than was formerly practicable.

It is one of the objects of this invention to provide an alternating current thermionic filament and cathode and none of the disadthe heater coating of silicon dioxide-accordtube of the indirectly heated cathode type the advantages of the solid dielectric between vantages thereof.

Another object of the invention is the provision of a means to balance out a portion of the magnetic-field which normally surrounds a filament energized by alternating current.

Another object of the invention is the provision of a long life filament for an indirectly heated cathode tube to heat the cathode to electron-emitting temperature in a minimum of time;

Another object of the invention is the provision'of a filament for an indirectly heated cathode which has a coating of high electrical insulation value and is not subject to deterioration due to cooling in spots.

Another object of the invention is the provision of an indirectly heated cathode tube in which the cathode is relatively close to the filament, thereby minimizing the time lag and affording a high thermal efiiciency of the tube. v

e Other objects of the invention and objects relating to methods of construction and means of supporting the various elements of the tube will be apparent from the description thereof.

As set out in my aforesaid co-pending application bearing Serial Number 398,550, I have discovered that a mixture of aluminum oxide (A1 0 and a Water solution of aluminum chloride (A101 provides an insulating material which readily adheres as a coating and which when baked and sintered, forms a tough, dense, hard and smooth layer that does not chip or flake. In preparing the mix.- ture, the crystallized aluminum oxide is finely ground and added to a 25% solution of aluminum chloride which is applied to the base in any suitable manner and then preferably heated to quickly evaporate the water. Upon a six mil. tungsten wire, a heating current of two amperes is adequate to dry the coating and make it adhere to the wire. After the application of each subsequent coating, the wire is further heated, the higher tempera ture serving to decompose the aluminum chloride and eliminate any hydroglelrli chloride by its substitution for oxygen. e important factor is involved in the oxychloride reaction The remaining solidmaterial is in aform which makes it the active or desired insulatin resistance material.

en a coating of five layers with a total thickness of about 4 mils. has been laid, the coated wire is cut into proper lengths and bent into shape, in the form of a loop or hair- P The insulation resistance depends upon the thickness of coating, the size of aluminum oxide crystals, the pressure between the coating and the cathode surface and the temperature applied.

crystallized aluminum oxide with aluml num chloride as the halogen compound to be dissociated is" preferred as the coating material but other halogen compounds, such as aluminum fluoride or bromide, or combinations of these ma be employed with aluminum oxide. lln p ace of the aluminum oxide component, other refractory oxides or oxide -com ounds such as beryllium or magnesium oxi e can be used with their halogen compounds or with aluminum chloride to obtain the oxychloride reaction which'is essential to form a hard integral layer without anyresidual binder.

In general, the fundamental requirement for the suspension material of this invention is to use a saltcapable of dissociatmg and displacing its halogen radical for oxygen, so as to leave only an active material which due 'to the almost infinitesimal size, builds up a material within the intercrystal spaces of the solid oxide, this condition giving a strength and insulation resistance,-otherwise not obtainable.

An embodiment of the invention is illustrated in the accompanying drawings in which I Fig.1 is a front elevation of the elements of a thermionic tube with portions broken away to show'more in detail the construc tion thereof.

Fig. 2 is a sectional plan view of the elements shown in Fig. 1.

Referring to thedrawings, the press P, supports the elements of the tube. To support anode 13, a pair of rods'14,'is sealed in the press P, and extends'upwardly in parallel. relation on either side of the anode. Support 4, is also sealed in the press .P, su port 11, being welded to that "support; t e helical grid 10, mounted concentrically within the plate is welded to support 11, which also serves partially to support glass plate 12. Plate 12, is also supported in part by ends of rods14, and b upright rod 9., on which lat-- ter is mounte a wire hook 9, for sufsprting the heater filament 2, at the loop en ereo "A tubular cathode-3,. is mounted concentrically within the grid and is connected at its top and bottom by means of members 5 and 7, respectively, which are welded to uprights 6 an 8 respectively, mounted paralle to the cathode, the former mounted in press P, the latter in glass plate 12.

A pair of supports 1, is sealed in the press P, at substantially the middle thereof and extends upwardly to a point adjacent the lower end of the tubular cathode 3. A hairpin heater filament 2, is mounted inside of the cathode 3, its lower ends being secured to the supports 1, one end of the filament being sc-. cured to one support and the otherend'being secured to t e other support. The filament is coated with an insulatlng material 3., composed of crystalline aluminum oxide which is so closely associated with the metal thereof as to. form a substantially integral structure with it.

The hook support 9., at the upper end or loop of the heater filament may be eliminated, the insulating coating on the filament being adequate to insure against leakage should "it contact with the adjacent cathode.

It may be desirable to coat the inside of the cylindrical cathode instead of the heater filament.

The construction as defined abovepermits theme of a metal filament which is, of ne-. cessity, relatively long with respect to the cathode, and permits a cathode of a relatively small diameter, and at the same time, provided a means to fix the potential of the cathode with respect to the filament, and also, means to balance out magnetic lines of force by the close proximity of the two legs of the fi ament, the current flowing in one leg in an opposite direction to the current flowing in t eother.

The spacing of theelemcnts shown in the drawing is somewhat exaggerated, as it is possible to provide a cathode of such small iameter that the clearance between the filament and the inner walls of the cathode is very minute as the nearer the cathode is placed to the filament, the quicker the heat resistance, and the greater the heat intercepted, while there is no danger of short circultirig, for even if the filament does touch the cathode, the insulating coating prevents such a short circuit.

Where a hairpin filament'is used, as indicated in-Fig. 1, a diameter of sixty-two thousandths (.062) inch will give suflicient clearance for both legs of the filament.

The cathode, of course, may be coated with a suitable electron-emitting substance, as is well understood in the art.

From the insulatin coating on the filament 1gases are easily riven ofi and there is a neg 'ble evolutionof gas or vapor from it,'so t at'little difiiculty is experienced in exhausting the tube; and theeflect as to time lag at initial heating of the filament is substantially the same as though no insulating material at all were used. By the -use of the heater insulation of my invention and the arrangement described herein the cathode is brought to electron emission temperature from room temperature in 6 to 7 'seconds instead of 45 to 60 seconds as required by the ceramic or other solid heater element.

dielectric about the Various modifications may be madein the construction as illustrated as by the elimina-- tion of members 9 and 9., and described-without departing from the spirit of the invention, which is intended, therefore, to be limited only by the scope of the appended claims.

YVhat I claim is:

1. In a thermionic tube of the heater type a tubular cathode, a hairpin heater filament within said cathode, means to support the two ends of said filament; and means integral with said filament to insulate said filament, from itself and from said cathode, said means comprising a coating composed of a refractory oxide mixed with a solution containing aluminum chloride and chemically combined in place upon said filament.

.2. In a thermionic tube of the heater type a tubular cathode, a hairpin heater filament within said cathode, means to support the two ends of said filament, and means integral with said filament to insulate said filament from itself and from said cathode, said means comprising a coating composed of aluminum oxide in a solution containing aluminum chloride and chemically combined in place upon said filament.

In a thermionic tube of the heater type a tubular cathode, a hairpin heater filament within said cathode, means to support the two ends of said filament, and means integral with said filament to insulate said filament from itself and from said cathode, said means comprising a coating composed of a refractory oxide mixed with a halogen salt of the same metal as the oxide capable of displacing its halogen component for oxygen and chemically combined in place upon said filament.

4. In a thermionic tube, a cathode, a heater filament adjacent said cathode, and an insulator composed of a refractory oxide mixed and chemically combined with a solution conta ining aluminum chloride closely allied to said filament and separating said filament and cathode.

5. In a thermionic tube, a cathode, a heater filament adjacent said cathode, and an insulator composed of aluminum oxide in a solution containing aluminum chloride, closely allied to said filamentand separating said filament and cathode.

6. In a thermionic tube, a cathode, a filamentaryheater adjacent said cathode and in close proximity thereto, and an insulating and integral with one or the material composed of a refractory oxide mixed with a' solution containing aluminum chloride between said cathode and filament other of's'aid cathode and filament.

7. In. a thermionic tube, a tubular cathode, a filamentary heater extending through said cathode, an insulating material composed of a refractory oxide mixed with a solution containing aluminum chloride integral witheither said heater or said-cathode to maintain said filament and cathode out of contact with each other. I '8. In a thermionic tube of the heater type a, tubular cathode, a heater filament within. said cathode, means to support the two ends of said filament, and means integral with. said filament to insulate said filament from itself and from said cathode, said means comprising a coating composed of a layer of crystalline aluminum oxide integrally formed on a refractory base heater.

I 9. In a thermionic tube, a tubular cathode,

a looped heater filament-within said cathode,

means to support the extreme ends of-said' filament, and means closely associated with said-filament to insulate said filament from itself and from said cathode, said means comprising a. coating composed of a layer of crystalline aluminum oxide integrally formed on a refractory base heater.

10. In a thermionic tube of the heater type, a tubular cathode, a' heater filament within said cathode, means to support the two ends of said filament, means integral with said filament to insulate said filament from itself and from said cathode, said means comprising a coating of crystallized aluminum oxide, said means being free of inactive binder.

11. In a thermionic tube of the heater type,

. a tubular cathode, a heater filament within said cathode, means to support the two ends of said filament and means integral with said filament to insulate said filament from itself and from said cathode, said means comprising a coating composed of a layer of crystalline magnesium oxide integrally formed on a refractory base heater 12. In a thermionic tube of the heater type, atubular cathode, a heater'filament within said cathode, meansto support the two ends of said filament and means integral with said filament to insulate said filament from itself and from said cathode, said means comprising a coating composed of a layer of crystalline beryllium oxide integrally formed on a refractory base heater.

13. In a thermionic tube, a tubular cathode, a looped heater filament within saidcathode, means to support the extreme ends of said filament and means closely associated with said filament to insulate said filament from itself and from said cathode, said means comprising a coating composed of a layer of crystalline magnesium oxide integrallyv formed on a refractory base heater.

14. In a thermionic tube, a tubular cathode, a looped heater filament within said cathode, means to support the extreme ends of said filament and means closely associated with said filament to insulate said filament from itself and from said cathode, said means comprising a coating com osed of a layer of crystalline beryllium oxide integrally formed on a refractory base heater.

15. In a thermionic tube of the heater type, a tubular cathode, a heater filament within of said filament, means integral with said filament to insulate said filament from itself and from said cathode, said means comprising a coating of crystallized ma nesium oxide, said means being free of Inactive binder. o

16. In a thermionic tube of the heater type, a tubular cathode, a heater filament within said cathode, means to support the two ends of said filament, means integral with said filament to insulate said filament from itself and from said cathode, said means comprisingv a, coating of crystallized beryllium oxide, said means being free of inactive binder.

17. An electron discharge" device having a cathode and an anode, a heater element with in said cathode, said heater element comprising a refractory filament having a coating composed of finely divided oxide crystals of the group consisting of aluminum oxide, beryllium oxide and magnesium oxide, the spaces between said oxide crystals being filled with an oxide of thesame group, formed in situ, of much finer particle size, said. coating being substantially integral with said filament. T

18. An electron discharge device having a cathode and an anode, a heater element with in said cathode, said heater element comprising a refractory filament having a coating composed of finely divided aluminum oxide crystals, the spacesbetween said oxide crystals being filled with an oxide of the group consisting of aluminum oxide, magnesium oxide and beryllium oxide, formed in; situ and of much finer particle size than saidfirst mentioned aluminum oxide, said coating being substantially-integral with said fila-- mcnt. Y

19. An electron discharge device having a cathode and an anode,'a heater element within said cathode, said heater element comprising a refractory filament having a coating composed of finely divided ma esium oxide crystals, the spaces between said oxide crystals being filled with an oxide of the group consisting of aluminum oxide, magnesium oxide and beryllium oxide, formed in situ and of much finer particle size than said first mentioned magnesiumoxide, said coating being substantially integral with said filament.

20. An electron discharge device having a cathode andan anode, a heater'element withment. said cathode, means to support the two ends '21. An electron discharge device having a cathode and an anode, a heater element within said cathode, said heater element compris ing a refractory filament having a coating composed of finely divided aluminum oxide crystals, the spaces between-said aluminum oxide crystals being filled with aluminum oxide, formed in situ, of much finer article size, said coating being substantially integral with said filament.

22. An electron discharge device having a cathode and an anode, a heater element within said cathode, said heater element comprising arefractory filament having a coating composed of finely divided magnesium oxide crystals, the spaces between said magnesium oxide-crystals being filled with magnesium oxide, formed in situ, of much finer particle size, said coating being substantially integral with said filament.

23. An electron discharge device having a cathode and an anode, a'heater element within said cathode, said heater element comprising a refractory filament having a coating composed of finely divided beryllium oxide crystals, the spaces between said beryllium oxide crystals being filled with beryllium oxide, formed'in situ, of much finer particle size, said coating'being substantially integral with said filament.

24. A refractory filamentary metal heating element for an electric tube device having a coating comprising a. mixture composed of an oxide of an element of the class comprising aluminum and beryllium and a halogen compound of one of said elements.

' 25. A- refractory filamentary metal heating element for an electric tube device having a coating comprising a mixture composed of aluminum oxide and a halogen compound of one of the elements aluminum and beryllium. 26. A refractory filamentary metal heating element for an electric tube device having a coating comprising a mixture composed of beryllium oxide and a halogen compound of one of theelements aluminunrand beryllium.

27: The method of preparing a heater element for an electric vacuum tube device which consists in coating a refracto metal filament with a plurality of layers 0 a mix ture compomd of an oxide of one of the elements, aluminum, magnesium and beryllium, and a halogen compound of one of said metals, and applying heat to the coating after the ap lication of each'of-said layers until the halogen content has been displaced by oxygen. I p

28. The method of preparing a heater element'for an electric vacuum tube device which consists in coating a refractory metal filament with" a plurality of layers of a mixture composed of aluminum oxide and a halogen compound of one. of the metals, aluminum, magnesium and beryllium, and applying heat to the coating after the application of each of said layers until the'halogen' content has been displaced by oxygen.

29. The method of preparing a heater ele ment for an electric vacuum tube device which consists in coating arefractory metal filament with a plurality of layers of amixture composed of magnesium oxide /and a halogen compound of one of the metals, aluminum, magnesium and beryllium, and ap plying heat to the coating after the applica tion of each of said layers until the halogen content has been displaced byoxygen.

30. The method of preparing a heater element for an electric vacuum tube device which consists in coating a refractory metal filament with a plurality of layers of. mixture composed of beryllium oxide and a halo-. gen compound of one of the metals, alumis num, magnesium and beryllium, and applying heat to the coating after the application of each of said layers until the halogen content has been displaced by oxygen.

31. The method of preparing a heater element for an electric vacuum tube device which consists in coating a refractory metal filament with a plurality of layers of a mixture composed of aluminum oxide and a halogen compound of aluminum and applying heat to the coating after the application of each of said layers until the halogen content'has been displaced by oxygen.-

32. The step in the manufacture of a heater element for an electric vacuum tube device which comprises applying to a refractory metal filament a coating composed of a mixture of an oxide of one of the metals, aluminum, magnesium and beryllium and a chloride of one of said metals, and thereafter dissociating said chloride by the application of heat to form an oxide of said metal.

33. The step in the manufacture of a heater element for an electric vacuum tube device which comprises applying to a refractory metal filament a coating composed of aluminum, oxide and a chloride of one of the metals, aluminum, magnesium and beryllium, and thereafter dissociating said chloride by the applilcation of heat to form an oxide of said meta metal filament a coating composed of magnesium oxide and. a chloride of one of the metals, aluminum, magnesium and beryllium, and thereafter dissociating said chloride by the application'of heat to form an oxide of said metal.

35. The step in the manufacture of a heater element for an electric vacuum tube device sociatingsaid chloride by the application of heat to form an oxide of aluminum.

In testlmony whereof, I, SAMUEL RUBEN, have signed m name to this specification,

this 21st day 0 October 1929.

SAMUEL RUBEN.

34. The step in the manufacture of a. heater element for an electric vacuum tube device whlch comprises applying to a refractory 

